TypeScript Generic Method Signature in Interface

Question

I am trying to define an interface with a few methods, and I would like one of the methods to be generic.

It is a filterUnique method, so it should be able to filter lists of numbers, strings, etc.

the following does not compile for me:

export interface IGenericServices {
    filterUnique(array: Array<T>): Array<T>;
}

Is there a way to make this compile, or am I making a conceptual mistake somewhere here?

Cheers!

thoughtrepo · Accepted Answer · 2015-09-21 21:25:16Z

37

The T type isn't defined yet. It needs to be added to the method as a type variable like:

filterUnique<T>(array: Array<T>): Array<T>;

Or added to the interface like:

export interface IGenericServices<T> {
    filterUnique(array: Array<T>): Array<T>;
}

answered Sep 21, 2015 at 21:25

thoughtrepo

8,4232 gold badges30 silver badges21 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

williaster Over a year ago

In case it helps others, you can also define a generic for the method of an interface without requiring the generic for the entire interface: interface MyInterface { method: <T>(arg: T): T; }

Wilt Over a year ago

@williaster If you would post that as an answer you would get my upvote, because that syntax was exactly what I was looking for when I landed on this page. Thanks! Small correction, change : to =>: <T>(arg: T) => T;

Christos Lytras · Accepted Answer · 2024-03-03 15:11:18Z

2

Making williaster's comment an answer as it also covers what many people are seeking for this question.

You can also define a generic for the method of an interface without requiring the generic for the entire interface:
interface MyInterface {
  method: <T>(arg: T) => T;
}

answered Mar 3, 2024 at 15:11

Christos Lytras

37.4k4 gold badges87 silver badges118 bronze badges

Collectives™ on Stack Overflow

TypeScript Generic Method Signature in Interface

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related